R Leaflet and Shiny - Example - Layers, Group and Layer Control along with markers

server.r

library(shiny) # load the shiny package
library(leaflet) # load the leaflet package 

# quakes dataset is used for this app. It comes with base R.
# ?quakes in R console to read more about the dataset
# str(quakes) 

# Classifying the type of earthquake based on magnitude as Light, Moderate, Strong or Major based on the magnitude range
quakes$type = ifelse((quakes$mag >= 4 & quakes$mag <= 4.9), "Light [4-4.9]",
                     ifelse((quakes$mag >= 5 & quakes$mag <= 5.9), "Moderate [5-5.9]",
                            ifelse((quakes$mag >= 6 & quakes$mag <= 6.9), "Strong [6-6.9]", 
                                   ifelse((quakes$mag >= 7 & quakes$mag <= 7.9), "Major [7-7.9]", "Great"      
                                   ))))



# Above Earthquake type based on it's magnitude is taken from http://www.geo.mtu.edu/UPSeis/magnitude.html
# By the end of this code, the quakes dataset will have one more column called type
# classification can be done in other ways as well.

# Color mapping using colorfactor()
# colorfactor() conveniently maps factor/char data values to colors according to a given palette.
pal = colorFactor(palette = c("yellow", "brown", "red"), domain = quakes$type)


# shiny server function begins here
shinyServer(function(input, output, session){
  
  output$mymap <- renderLeaflet({
    # mapping the quakes
    mymap = leaflet(data=quakes) %>% # initialize the map ad dataset to be used
    
      # add 3rd party tile
      addProviderTiles("Esri.WorldImagery") 
    
    
    # Below code will add circle markers and groups based on types.
    # Create groups within the addCirleMarkers. Subsetted data is used for individual groups
    for(t in unique(quakes$type)){ # loop through each of the types we defined earlier
      sub = quakes[quakes$type==t,] # subset the data based on each type
      mymap=mymap %>% 
        # add Circlemarker
        addCircleMarkers(
          data=sub,
          lng =  ~ long,
          lat =  ~ lat,
          radius = 5,
          color =  ~pal(type),
          stroke = FALSE, 
          fillOpacity = 0.5,
          label= paste(
            "Magnitude: ", sub$mag, "Type:", sub$type, "Depth: ", sub$depth, "Stations: ", sub$stations,
            sep = ""
          ),
          group = t
        ) 
        
    }
      
      
      # Below code to add control layers and legend to the map.
      mymap %>% 
  
      addLayersControl(
        overlayGroups = unique(quakes$type),
        options = layersControlOptions(collapsed = FALSE)
      ) %>% 
      
        
      # add legend to the map
      addLegend(
        position = "bottomright",
        pal = pal,
        values = ~ type,
        title = "Type based on magnitude",
        opacity = 0.3
      )
    
  })
  
})

ui.r

library(shiny)
library(leaflet)
shinyUI(bootstrapPage(
  h4("Mapping location of earthquakes off Fiji from quakes dataset"),
  h5("The data set give the locations of 1000 seismic events of MB > 4.0. The events occurred in a cube near Fiji since 1964. 
     These are sample from a larger dataset of 5000 observations."),
  leafletOutput("mymap", height = "600")
  ))